Bug 30194: (26351 follow-up) Silence useless warning

Bug 30194: (26351 follow-up) Silence useless warning

Every place in which Koha::Plugin::Test is loaded, and a patron is
updated, this hook needs to be silenced.

To reproduce:
1. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/REST/Plugin/PluginRoutes.t
=> FAIL: There's a warn about patron_barcode_transform
2. Apply this patch
3. Repeat 1
=> SUCCESS: Tests pass!
4. Sign off :-D

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Mason James <mtj@kohaaloha.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>